Why is it so hard to add a removeable back cover to have swappable battery? Seemingly battery replacement can still be done "in 5 minutes" but this still makes pop-out/on the road battery swapping unpractical. https://www.trustedreviews.com/reviews/nokia-g22
But then thickness and aesthetic "cheapness" is a secondary one.
A removeable cover and battery is always going to introduce a little bit of thickness, which on a thin phone is noticeable even if not major.
And then whether you have screws or the ridges for removing the cover, it just always feels a little "cheap". You can't get the same kind of rounded smooth glass or aluminum backing that wraps seamlessly around the edges.
And when people are comparing two phones in their hands, the one that feels more "premium" is often the one they'll go with if they feel they're already paying a premium price. This is an object they hold in their hand all day long. And if you live in a major city, it's really not a big deal to get your battery replaced after 2 years at an Apple Store.